If I was you, I'd try sticking with the stichodactyla family. Try a maxi or mini carpet, a cousin. Not only a real good chance of compatability, but they come in some nice colors too! ...they stay small..... Maxi around 8" max, and mini maybe 2, 3, or 4" max, I think. ?..problem may be splitting if they're happy.... I'm not familiar with keeping them first hand, but from what I've seen, they seem to work well with the rest of the stichodactyla's.
It's too hard for anyone to say for sure that you would have trouble adding an anemone, but adding some specific ones, like a mag or LTA for example, is asking for trouble, depending on type, size, etc.... A very broad question..... Best of luck, post a pic of your haddoni pl